1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Stupid useless #%!@! chem equations

  1. Oct 3, 2004 #1

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As you can tell, not my favorite subject. :grumpy: I was going along fine just tinkering with these things and working them out until I started trying to balance this one:

    Ca3(PO4) + H2SO4 -> CaSO4 + H3PO4

    The coefficients I have tried so far are:

    2Ca3(PO4) + 3H2SO4 -> 6CaSO4 + 2H3PO4

    so on LHS I have
    6 Ca, 2 P, 20 O, 6 H, 3 S
    and on RHS I have
    6 Ca, 2 P, 32 O, 6 H, 6 S

    (I think.. :confused: )

    I wasn't sure if I needed to keep going and trying different or larger coefficients or if I have already gone wrong somewhere.

    Also, if anyone has any tips for balancing these things I'd be glad to hear them. My teacher didn't give any formal procedures for working with these. Thanks. :smile:
     
  2. jcsd
  3. Oct 3, 2004 #2
    Is there a coefficient on PO4 on the left side? Ca3 has a +6 charge in ion form..

    Edit: The equation you posted I don't believe is balanceable. Trying to come up with a linear system to prove this.

    Double edit: If there's a 2 subscript on the PO4, 1, 3, 3, 2 balances it left to right.
     
    Last edited by a moderator: Oct 3, 2004
  4. Oct 3, 2004 #3

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Hi vsage, thanks for responding. I am double checking the worksheet again... no, that's exactly how the equation appears.
    Possibly the worksheet itself contains a typo?
    I should mention that this is a class for "non-science majors", so the balancing should not be a difficult matter, I would assume...? Everything else has been beginner level.
     
  5. Oct 3, 2004 #4
    I am 100% confident there should be a 2 subscript on the PO4 on the left side. Every compound in the equation has to be electrically neutral and in order for Ca3(PO4) to be electrically neutral (PO4) must have a charge of -6. However if you look on the right side, there's H3(PO4) which has to be electrically neutral so I'd figure a P04 ion actually has a -3 charge.

    Don't worry: I feel your pain. I hated AP chem so much last year. Studied my butt off and only got a B equivalent :( Shame on the sheet for having a typo.

    Edit: It would not be unwise to wait for a second opinion though. I have been known to be wrong before but probably not on one of this difficulty (or rather facility)
     
    Last edited by a moderator: Oct 3, 2004
  6. Oct 3, 2004 #5

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Thank you for taking the time to look at this. I'll post back after I have class again and let you know what I found out! :smile:
     
  7. Oct 3, 2004 #6

    plover

    User Avatar
    Homework Helper

    I second vsage. Even the notation that is there indicates that something is missing. I.e. why the parentheses in
    Ca3(PO4)​
    if the PO4 isn't supposed to have a subscript. Plus a phosphate ion has charge -3. So:
    Ca3(PO4)2
     
    Last edited: Oct 3, 2004
  8. Oct 3, 2004 #7

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Something must be awry on the worksheet. I was hoping that maybe I was misunderstanding the meaning of the parenthesis, and that would explain it, but that doesn't seem to be the case.
     
    Last edited: Oct 3, 2004
  9. Oct 3, 2004 #8

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    while we're at it...

    OK, while we're on the subject, let me ask this:
    If you see parenthesis in a compound like Ba(OH)2, why are those parentheses there?
    I am treating it just as if it were written BaO2H2 when I do the balancing. Is this correct? I am assuming there are two hydrogen atoms and two oxygen atoms.
    Thanks!
     
  10. Oct 3, 2004 #9
    OH is a hydroxyl ion
    Ba(OH)2 is basically a ionic bond with positive ion Ba and negative ion OH
    so u see why OH is grouped together

    i don't see any problem with that ..... ofcourse i cannot get pedantic abt it as i am not a chemist , yet seeing it as 2 oxygen and 2 hydrogen is fine .... still as far as the arrangement of ions is concerned , denoting the hydroxyl ion as (OH) is a must.

    -- AI
     
  11. Oct 3, 2004 #10
    I wouldn't get rid of the parenthesis because some polyatomic ions (like SO4) don't balance right if you break them up into their components because that ion forms covalent bonds to eliminate excessive negative charge. If you were to treat it as S1O4 then the overall charge would be -10 assuming all ions but in actuality when it's a polyatomic ion it's -2. I'd like to point out with hydroxide ions (OH-) the polyatomic ion's charge is equal to the sum of the indididual elements in ion form so you are not incorrect for that particular case but you can't always do that.
     
    Last edited by a moderator: Oct 3, 2004
  12. Oct 3, 2004 #11

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    OK, thanks, y'all. I just wanted to make sure I was counting the atoms correctly and that the subscript 2 outside the parenthesis meant 2 Oxygen and 2 Hydrogen. It's the distribution of that 2 that I was concerned about.
     
  13. Oct 3, 2004 #12

    plover

    User Avatar
    Homework Helper

    There are two separate issues here. In terms simply of the number of individual atoms involved in the reaction, (OH)2 does correspond to 2 0 and 2 H. However, a group of atoms which forms a stable ion such as OH- or PO4-3 or SO4-2 will act as a single unit in the reaction and should be thought of as such. This is especially true in cases such as vsage mentioned, where treating the atoms separately would suggest a misleading assessment of the charges involved.
     
  14. Oct 3, 2004 #13

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    What are the superscripts? Do those denote charges?
     
  15. Oct 3, 2004 #14
    Well it depends on whether the sign is on the front or the back of the number. I think sign on back of a superscript is charge and sign on front is oxidation number but it's been a year since I took chem.

    Edit yeah I wouldn't worry about it in any case you're not dealing with oxidation/reduction reactions for several weeks (if this semester)
     
    Last edited by a moderator: Oct 3, 2004
  16. Oct 3, 2004 #15

    plover

    User Avatar
    Homework Helper

    In my post, yes, they denote charges. And while I do recall seeing both SO4-2 and SO42- as notations, I don't recall being taught that there was a difference between the two, which of course may just mean that I don't remember or may mean that the distinction is not used universally. A cursory googling did not clear this up. I suspect that if you ever need to treat them differently it will be made clear.

    Sometimes the charge is indicated by a series of - or + instead, like this:
    PO4---
     
    Last edited: Oct 3, 2004
  17. Oct 3, 2004 #16
    vsage is right. But I am assuming ox/reduct is far in your future (next semester, if even then for a non major chem class).

    All you need to remember is superscripts denote charges, subscripts denote numbers of, and there SHOULD have been a subscript after those parenthesis. Appears to be a simple typo to me.

    Chemistry I know, Physics kicks my tail.
     
  18. Oct 3, 2004 #17

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Actually, I hoping it's not in my future! :rofl: I am definitely trying to get by with the minimum chem knowledge possible.
     
  19. Oct 7, 2004 #18

    Math Is Hard

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Update!

    Yes! It was a typo!!!!!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Stupid useless #%!@! chem equations
  1. Simple chem equation (Replies: 3)

  2. Stupid question (Replies: 2)

  3. Stupid Charges (Replies: 6)

Loading...